1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) and a driving method thereof, and more particularly, to an LCD wherein driving stability can be secured and a driving method for such an LCD.
2. Discussion of Related Art
In recent years, various types of flat panel displays that have a lower weight and volume than cathode ray tubes (CRTs) have been developed. Liquid crystal displays (LCDs), field emission displays (FEDs), plasma display panels (PDPs), organic light emitting displays (OLEDs) and the like are used as flat panel displays.
Since LCDs have advantages in terms of miniaturization, lightweight, low power consumption and the like, they have been gradually highlighted for replacing the existing CRTs. At present, LCDs have been used not only in portable devices such as cellular phones and Personal Digital Assistants (PDAs) but also in large and medium sized devices such as monitors and TVs.
In an LCD, liquid crystal is injected between an upper substrate having a common electrode and the like formed thereon and a lower substrate having a thin film transistor, a pixel electrode and the like formed thereon. Different electric potentials are applied to the pixel electrode and the common electrode so that an electric field is formed therebetween. The arrangement of the liquid crystal between the upper and lower substrates is changed due to the electric field between the pixel and the common electrodes, and thus an image is displayed while transmittance of light is being controlled.
Among the LCDs, an Optically Compensated Birefringence (OCB) mode LCD has the advantages of a wide viewing angle and a high response speed. Therefore, the OCB mode LCD is being actively studied.
As shown in FIGS. 1A and 1B, in an OCB mode LCD, liquid crystal injected between an upper substrate 10 and a lower substrate 12 is initially set to be in a splay state where a voltage V smaller than a transition voltage Vcr is applied to the liquid crystal (V<Vcr). In such a splay state, light is irregularly transmitted as the voltage V increases. Accordingly, in the splay state, unevenness or flicker is produced on an image.
If a voltage V larger than a transition voltage Vcr is applied to the liquid crystal in the splay state, the liquid crystal is converted into a bend state (V>Vcr). In such a bend state, the transmittance of the liquid crystal is linearly decreased as the voltage V increases. Thus, in a conventional OCB mode LCD, a voltage larger than the transition voltage Vcr is applied to liquid crystal cells to convert the liquid crystal into the bend state, and a predetermined image is then displayed.
However, in the conventional OCB mode LCD, the liquid crystal of some of the liquid crystal cells forming the LCD panel returns from a bend state to a splay state. In practice, the liquid crystal returning from the bend state to the splay state mainly occurs in the liquid crystal cells located at the outermost edges of the LCD panel. It can be speculated that these liquid crystal cells do not sustain their bend states because the liquid crystal cells located at the outermost edges of the LCD panel are not affected by the surrounding electric field.